Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 221135
AFDUNR

Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
435 AM MST Wed Feb 22 2017

.SHORT TERM...(Today Through Thursday Night)
Issued at 435 AM MST Wed Feb 22 2017

Current surface analysis shows low pressure over central SD, with
cold front now through most of the forecast area except for south
central SD. Upper level analysis shows shortwave energy crossing
eastern MT, western ND, and northwest SD, with a few showers
across far northwest SD. Next system to impact the area late this
week is moving into the Pacific Northwest now. Earlier shower
activity over west central and southwest SD has moved east of the
region. Skies are mainly cloudy in most areas, with some clearing
across far southern SD. Temps are in the upper 30s and 40s most
areas, a bit cooler across the higher Black Hills. Winds are west-
northwest behind the front, southwesterly ahead of it.

Cooler weather today, though still above average, with highs in the
mid 40s to mid 50s. Clouds will decrease across the southern half of
the forecast area later this morning, with mostly cloudy conditions
lingering across northwest SD, along with isolated to scattered
showers. Clouds will settle over the entire area tonight as the
upper level system to the west moves into the Rockies. Strong
shortwave energy ahead of the system will move into western and
southern portions of the forecast area overnight, with snow
spreading across much of northeast WY into southwest SD after
midnight. Colder air building into the area will change any initial
rain over to snow quickly as temps drop to the mid 20s to lower 30s
by daybreak.

Latest model runs on this system continue to show a stronger upper
level system as it crosses the plains, and as a result a more
northerly track, compared to previous nights. EC and GFS are in
pretty good agreement, with the GFS a bit stronger than the EC as
the upper low passes east of the area. Surface low is also a bit
further north and stronger as it moves across KS Thursday then
shifts into the upper midwest Thursday night and Friday, which will
result in some stronger winds, especially toward south central SD.
NAM is actually slightly further north than the others after being
the furthest south earlier yesterday. Canadian is now the furthest
south of the group.

Needless to say, there is still some uncertainty on the exact track
and where the heaviest snowfall will occur, but the most likely
areas at this point are from southern portions of northeast WY and
east central WY to far southern SD and northern Neb, where a foot or
more of snowfall is a possibility. The heaviest snowfall in most
areas will generally be during the daytime hours Thursday and into
Thursday evening, possibly to early Friday over south central SD.
Have extended the watch area slightly further north to account for
northern shift and increased potential for around 6 inches of
snowfall near and along the I-90 corridor across western SD.

.LONG TERM...(Friday Through Tuesday)
Issued at 435 AM MST Wed Feb 22 2017

Snow will taper off across the area Friday morning as low
pressure moves quickly into the upper midwest, with lingering
areas of light snow possible through the afternoon across mainly
southern portions of the forecast area. Gusty winds east of the
Black Hills could continue to produce at least patchy blowing snow
through the afternoon.

Mostly dry weather is expected over the weekend and Monday as drier
northwest flow is in place. Weak disturbances will bring clouds and
the possibility for snow showers at times, mainly across far
northeast WY, the Black Hills, and northwest SD. Temperatures will
generally be slightly below average Friday through Monday, highs
mostly in the mid 20s to mid 30s. The next upper level system will
likely impact the region Monday night and Tuesday. This system is
showing a more northerly track across the Northern Plains at this
time, which would bring the better chances for snow across northeast
WY, northern SD, and locations further to the north.

&&

.AVIATION...(For the 12Z TAFS Through 12Z Thursday Morning)
Issued At 435 AM MST Wed Feb 22 2017

VFR conditions are generally expected today and into this
evening. Shortwave energy passing mostly across eastern MT and ND
will bring a chance for rain showers across northwest SD today.
The next storm system will begin to impact the area after 06z
tonight, with snow moving into northeast WY and southwest SD.
MVFR/IFR conditions will develop across these areas, with areas of
LIFR conditions expected by 12Z, especially across southern parts
of northeast WY and far southwest SD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from late tonight through Friday morning for
     SDZ027-029-030-041-042-044-074.

     Winter Storm Watch from Thursday morning through Friday morning
     for SDZ024>026-028-031-032-043-046-047-049-072-073.

WY...Winter Storm Watch from late tonight through Friday morning for
     WYZ055-058.

&&

$$

SHORT TERM...26
LONG TERM...26
AVIATION...26



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